The present invention concerns a method, in the wider concept of claim 1, an apparatus, for singularizing the fuel rods of a fuel element.
It is well known that a fuel element consists of a larger number of individual fuel rods. Such fuel rods comprise closed tubular cans containing nuclear fuel as well as a smaller number of control or absorber rods. With the help of spacers, which are arranged in the form of a grid cage, of a head piece, and of a foot piece, the fuel rods and the control rod guide tubes are arranged in a square matrix. Spent fuel elements are stored in the storage pool of the reactor or in storage containers, before reprocessing or final disposal. The spent fuel rods require a great deal of storage space in the matrix arrangements. Thus, it is desirable that the storage facility be as compact as possible. However, the fuel rods have to be singularizer for compact storage.
An apparatus is known from document EP-A No. 0066695 for consolidating spent fuel rods of fuel elements, which is provided with a fuel element head. The fuel element head is connected to control rod guide tubes. The fuel rods are maintained at a distance from one another by means of spacers. The foot of the fuel element can be firmly clamped in this arrangement. With the help of an arrangement of internal cutters, comprising a cutting tool, the head parts of the control guide tubes can be severed and removed together with the head itself. With the help of a grappler arrangement, the fuel rods can then be extracted and transferred to a consolidating stage. The consolidating stage is provided with guide tubes, one end of which is arranged in a first rack in exactly the same way as the fuel rods in the fuel element. The fuel rods themselves are inserted in the guide tubes. At their other end, the guide rods extend through a second rack in which they are arranged in a more compact way. The fuel rods are then advanced out of the guide tubes into a horizontal arrangement in which they are further consolidated and they are finally inserted in an arrangement in which they are consolidated vertically. After horizontal and vertical consolidation, the fuel rods are then placed in storage containers. This known arrangement is relatively complex. Moreover, the arrangement requires a great deal of space, since extra space has to be found corresponding to, the extended length of the rods. Since the guide tubes are positioned at an angle between the two parts of the rack and are bent along part of their length, there is always the danger of fracturing the fuel rods while they are being inserted into or extracted from these guide tubes.
An arrangement is shown in document U.S. Pat. No. 2,853,625 for unloading a number of spent uranium fuel rods from a reactor. The reactor is provided with a charging and a discharging side, whereby the rods are arranged in cladding tubes. This arrangement consists of a trolley which can travel both vertically and horizontally. The trolley is provided with a storage chamber partially filled with water. The trolley is also provided with a pick-up nose which can be aligned with a cladding tube. To expel the spent uranium rods, fresh fuel rods are inserted in the cladding tube on the charging side of the reactor. The spent uranium fuel rods are then pushed into a channel in the charging stage of the trolley on the discharge side of the reactor. The free end of the expelled spent rods is taken up by a piston which travels through the chamber under hydraulic power. The channel ends in this storage chamber. As soon as the end of the spent rod reaches the end of the channel, it will fall into the storage chamber. This process is repeated until the required number of uranium rods has dropped into the storage chamber. The increased space and complexity of this design are disadvantageous features of this arrangement. In particular, an extra chamber is required for the extraction of the fuel rods, and the chamber has to be at least twice the length of the rods. Furthermore, in this known singularizer process, there is always the risk of fracturing the rods as they are pushed out of the cladding tube or the channel of the pick-up nose as well as when they fall into the storage chamber.
In document DE-OS No. 27 30 723, an apparatus and a process are described for space saving disposal of channels for radioactive fuel material. With the help of a cutting arrangement, the square-sectioned empty metal tubular channels are cut open in a water bath. This produces four individual side plates, which can be placed on top of one another in a storage container to save space. This document, however, provides no indication of how the fuel is removed from the channels.
Document DE-PS No. 17 64 523 provides a description of an arrangement for severing the inert end zones of a fuel element in order to remove the nuclear fuel from the casing enclosed by the inert end zones. This cutting arrangement is provided with a holder to maintain the fuel element horizontally. The cutting arrangement takes the form of a band saw at each end zone. This holder can be moved towards the band saws so that both end zones can be pushed toward the band saws and can be cut off at the same time. However, this document does not contain any indication of how the fuel is removed from the casings, either.